The present invention relates to plugs for gripping and forming fluid-tight seals with inner or outer peripheries of pipes, pipelines, tubes, pressure vessels and the like adjacent open ends thereof. More specifically, the present invention relates to components of plugs enabling the plug to grip and/or bite into the inner or outer diameter of pipe or tube walls and/or to withstand differential pressure across the seal created by the plug. For purposes of example, the plugs may include hydrostatic test plugs, vacuum test plugs or the like for use in pressure testing pipes, pipelines, tubes, pressure vessels, pressure retaining components, and the like and isolation plugs for use in isolating segments of pipes and tubes for any reason such as painting or the like, for forming night caps, for hydrostatically testing weld joints of welded flange-to-pipe connections, and for isolating pipe or tube ends during cutting, grinding and/or welding operations.
It is often required to perform leak tests or verify structural integrity or strength of pipes, pipelines, tubes, pressure vessels, flange-to-pipe connections, pipe-to-pipe connections, and the like. It may also be necessary to isolate the open end of a pipe from vapors that may be contained within the pipe when performing operations adjacent the end of the pipe, such as adding a flange or making some other pipe connection. For example, a pipe may need to be temporarily sealed adjacent to an open end thereof and pressurized with a fluid such as gas, including air or nitrogen, or a liquid such as a hydraulic fluid. Depending upon the material and thickness of the pipe, the pipe may be pressure rated, and a test or isolation plug used to form one or more seals adjacent an open end of the pipe must be able to withstand at least the pressure rating of the pipe and must be able to resist movement, sliding, failure, blow-out and/or leakage during such working pressures.
High-pressure test and isolation plugs may include components configured to be urged radially outward into engagement with an inner peripheral wall of a pipe or tube or radially inward into engagement with an outer peripheral wall of a pipe or tube. A gripping function is required to enable the plug to resist movement, sliding, failure, blow-out and/or leakage during testing at working pressures. Any movement of the plug or its gripping components relative to the sealed pipe must be avoided, particularly when testing at high pressures.